The overall objective of this Project is to determine if the outcome of allogeneic transplantation for hematologic malignancies can be improved through the use of growth factor mobilized peripheral blood stem cells (PSBCs) instead of marrow. Initially, a prospective randomized trail will be performed in patients with a variety of hematologic malignancies undergoing transplantation from matched siblings in which the outcome using unmodified G-CSF mobilized PBSCs will be compared with that using marrow. If the results demonstrate that PBSCs lead to more rapid engraftment without a significant increase in graft-versus-host disease (GVHD), the trail will be continued in patients with a single hematologic malignancy, chronic myeloid leukemia. Additional studies will be carried out examining if the results of transplantation using PBSCs can be further improved by partial T cell depletion. Specifically, clinical studies will be conducted based on animal experiments demonstrating that engraftment without GVHD can be achieved with complete CD4 and partial CD8 depletion. The results of these studies should define the optimal stem cell product for use in matched sibling transplantation.